7. Abstract/Project Summary Each year since 2009, more than 28,000 people have received organ transplants in the United States. Immunosuppressive medications are critical to reduce rejection and graft loss in transplant recipients. These medications can be expensive and pose a financial burden to patients, leading to non-adherence. Substituting costly brand name medications with therapeutically equivalent, less expensive generic medications is a potential solution to overcome the financial barrier and improve access and adherence to immunosuppressants. However, there are questions regarding the therapeutic equivalence of generic and brand name immunosuppressants. In addition, generic products have not been compared with each other; thus, there is a concern regarding the substitution of one generic for another generic. This uncertainty is problematic for clinicians who seek to provide the best care for their patients. To examine the utility of generic immunosuppressants, we will study recipients of kidney and liver transplants between 2008 and 2013. The first of three specific aims of the project is to describe patterns of generic and brand immunosuppressant use after transplant. These patterns will be examined for patients by time since transplant and also by calendar date, to carefully tease apart changes that occur as patient needs evolve from changes that coincide with changes in the availability of generic immunosuppressants. We will describe patterns at the level of the transplant program, aggregated across patients, to understand program-level factors associated with the speed of generic immunosuppressant adoption. To address our second specific aim, we will compare risks of biopsy-proven and treated rejection and graft failure for patients on generic and brand name immunosuppressants. We will use time-dependent Cox regressions to model these risks, controlling for variability between recipients, organ donors, and characteristics of the transplant surgery. We will carefully examine heterogeneity of treatment effects in patient subgroups, including pediatric patients and adults, racial and ethnic minorities, women and men, and patients with medical complexities or greater- than-average risk for adverse outcomes. Assuming we find no meaningful difference in the effectiveness of generic medications relative to brand name medications, our third aim will be to quantify the costs associated with each type of medication. We will demonstrate the savings to patients and to payers through the use of generic immunosuppressants in place of brand name immunosuppressants. Ultimately, we expect that this study will provide significant new insights regarding the use of generic and brand name immunosuppressants, leading to improved care for transplant recipients.